It is the first known copy of the most famous painting in history, and a discovery that curators believe sheds new light on the creation of the masterpiece.

Deputy conservator, Gabriele Finaldi, said: “It’s as if we were standing in the workshop itself, and at the next easel. You can see that the artist was working step by step with Leonardo. When Leonardo made a change, he made a change.”

The copy sits in a dimly-lit room awaiting the finishing touches of a two-year restoration, during which its true origin was revealed. Curators decided it needed a face lift because it was going on loan to the Louvre in March. Following X-ray and infrared studies, they were surprised to find a landscape hidden beneath the dark paint behind the subject.

Conservators believe the artist could be Francesco Melzi, one of Leonardo’s favourite pupils. “When you look at the copy, you can imagine that this is what the Mona Lisa looked like in the 16th century,” Mr Finaldi continued. “It’s not just the details and the colour use. It has also been protected from light and dirt for centuries. So what you see if a very reliable appearance.”

The Mona Lisa is widely believed to be a portrait of Lisa Gherardini, a Florentine merchant’s wife, and the copy makes her look younger and more seductive.

An Italian researcher has sparked new controversy over the world’s most famous painting by claiming Leonardo da Vinci painted tiny letters into the eyes of the Mona Lisa which may finally reveal the disputed identity of his model.

To arrive at a theory worthy of The Da Vinci Code, Dan Brown‘s 2003 bestseller, researcher Silvano Vinceti avoided the Mona Lisa‘s enigmatic smile and instead gazed deep into her eyes with the help of high-resolution images.

“Invisible to the naked eye and painted in black on green-brown are the letters LV in her right pupil, obviously Leonardo’s initials, but it is what is in her left pupil that is far more interesting,” said Vinceti, the chairman of the Italian national committee for cultural heritage.

Vinceti said that the letters B or S, or possibly the initials CE, were discernible, a vital clue to identifying the model who sat for the Renaissance artist. She has often been named as Lisa Gherardini, the wife of a Florentine merchant, but Vinceti disagreed, claiming Leonardo painted the Mona Lisa in Milan. He said he would announce his conclusions next month.